The technical principle of forward osmosis (FO) desalination process utilizes an osmosis pressure difference (between two solutions/solutes in two parts separated by a semi-permeable film) as a driving force. Water in a feed part with a lower osmosis pressure will permeate through a semi-permeable film to enter a draw solution part with a higher osmosis pressure. The mixture liquid of the water (permeating through the semi-permeable film) and the draw solution can be separated or concentrated to separate the water and the draw solution, thereby recycling the draw solution and producing pure water. In water treatment, the forward osmosis process has advantages such as low energy consumption and low film fouling ratio, which may largely enhance the function stability and cost effectiveness.
The draw solution should have the properties of (1) high osmosis pressure, (2) hydrophilicity, and (3) being easily separated from water, in which the separation of the draw solution and the water (through the semi-permeable film) and the recycling of the draw solution are critical factors of energy consumption in the forward osmosis process. Some conventional skills adopts an ionic liquid to serve as draw solute, but the draw solution (mixture liquid of the water and the ionic liquid) should be heated to 35° C. to 50° C. to separate into two layers (water layer and ionic liquid layer). Obviously, the conventional methods using the ionic liquid have the problem of energy consumption due to necessary heating.
Accordingly, a novel draw solute for the forward osmosis process is still called for to solve the problem described above.